Finite-time Response of Dynamo Mean-field Effects in Magnetorotational Turbulence
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Finite-time Response of Dynamo Mean-field Effects in Magnetorotational Turbulence. / Gressel, Oliver; Pessah, Martin E.
In: Astrophysical Journal, Vol. 928, No. 2, 118, 01.04.2022.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Finite-time Response of Dynamo Mean-field Effects in Magnetorotational Turbulence
AU - Gressel, Oliver
AU - Pessah, Martin E.
PY - 2022/4/1
Y1 - 2022/4/1
N2 - Accretion disk turbulence along with its effect on large-scale magnetic fields plays an important role in understanding disk evolution in general, and the launching of astrophysical jets in particular. Motivated by enabling a comprehensive subgrid description for global long-term simulations of accretions disks, we aim to further characterize the transport coefficients emerging in local simulations of magnetorotational disk turbulence. For the current investigation, we leverage a time-dependent version of the test-field method, which is sensitive to the turbulent electromotive force (EMF) generated as a response to a set of pulsating background fields. We obtain Fourier spectra of the transport coefficients as a function of oscillation frequency. These are well approximated by a simple response function, describing a finite-time buildup of the EMF as a result of a time-variable mean magnetic field. For intermediate timescales (i.e., slightly above the orbital frequency), we observe a significant phase lag of the EMF compared to the causing field. Augmented with our previous result on a nonlocal closure relation in space, and incorporated into a suitable mean-field description that we briefly sketch out here, the new framework will allow us to drop the restrictive assumption of scale separation.
AB - Accretion disk turbulence along with its effect on large-scale magnetic fields plays an important role in understanding disk evolution in general, and the launching of astrophysical jets in particular. Motivated by enabling a comprehensive subgrid description for global long-term simulations of accretions disks, we aim to further characterize the transport coefficients emerging in local simulations of magnetorotational disk turbulence. For the current investigation, we leverage a time-dependent version of the test-field method, which is sensitive to the turbulent electromotive force (EMF) generated as a response to a set of pulsating background fields. We obtain Fourier spectra of the transport coefficients as a function of oscillation frequency. These are well approximated by a simple response function, describing a finite-time buildup of the EMF as a result of a time-variable mean magnetic field. For intermediate timescales (i.e., slightly above the orbital frequency), we observe a significant phase lag of the EMF compared to the causing field. Augmented with our previous result on a nonlocal closure relation in space, and incorporated into a suitable mean-field description that we briefly sketch out here, the new framework will allow us to drop the restrictive assumption of scale separation.
KW - ROTATING MAGNETOCONVECTION
KW - SHEARING BOX
KW - IMPLEMENTATION
KW - SIMULATIONS
KW - INSTABILITY
KW - SATURATION
KW - PATTERNS
KW - I.
U2 - 10.3847/1538-4357/ac56dd
DO - 10.3847/1538-4357/ac56dd
M3 - Journal article
VL - 928
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - 118
ER -
ID: 303443693